The invention relates generally to instruments for use in orthopedic surgical implantation procedures and more specifically to an apparatus for inserting an implant between vertebral bodies.
The bones and connective tissue of an adult human spinal column consists of more than twenty discrete bones coupled sequentially to one another by a tri-joint complex which consists of an anterior disc and the two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs. These more than twenty bones are anatomically categorized as being members of one of four classifications: cervical; thoracic; lumbar; or sacral.
Genetic or developmental irregularities, trauma, chronic stress, tumors, and degenerative wear are a few of the causes that can result in spinal pathologies for which surgical intervention may be necessary. A variety of systems have been disclosed in the art which achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back that needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, and the insertion of implants and/or height restorative devices, several methods and devices have been disclosed in the prior art.
More particularly, and with respect to the historical development of the present surgical methods and instrumentations, the description of the relevant medical techniques are now described. Failure of the intervertebral disc cartilage generally includes a loss of proper anatomical spacing between the end plates of the opposing vertebral bodies. This loss of height may simply destabilize the spine, or, in severe cases, it may cause considerable neurological impairment as the nerve roots are compressed by the converging lateral extensions of the bones (e.g., in the facet joint).
Restoring the appropriate height to the intervertebral space is the first step in the surgical strategy for correcting this condition. Once this is achieved, one class of surgical implantation procedures involves positioning a device into the intervening space. This may be done through a posterior approach, a lateral approach, or an anterior approach. Various implant devices for this purpose include femoral ring allograft, cylindrical metallic devices (e.g., cages), and metal mesh structures that may be filled with suitable bone graft materials. Some of these implant devices are only suitable for one direction of approach to the spine. All of these devices, however, are provided with the intention that the adjacent bones will, once restored to their appropriate separation, then grow together across the space and fuse together (or at least fuse into the device implanted between the bones).
Most recently, the development of non-fusion implant devices, which purport to permit continued natural movement in the tri-joint complex, have provided great promise. The instrumentation and methods for the implantation of these non-fusion devices, as well as the implantation of the fusion devices catalogued previously, therefore should integrate the functions of restoring proper anatomical spacing and easing insertion of the selected device into the formed volume.
To these ends, several instruments for such implantation have been described in the prior art. These include U.S. Pat. No. 6,159,215 to Urbahns, et al. (xe2x80x9cUrbahnsxe2x80x9d), U.S. Pat. No. 6,042,582 to Ray (xe2x80x9cRayxe2x80x9d), and U.S. Pat. No. 5,431,658 to Moskovich (xe2x80x9cMoskovichxe2x80x9d). More particularly, Ray describes a device and method of implantation for use specifically with cylindrical cage devices that are inserted such that the axis of the implant device is perpendicular to the axis of the spine. The reference teaches the use of a series of similarly shaped plugs to be inserted posteriorly between the collapsed bones, for the purposes of separating the adjacent bones, followed by the cutting of the endplates to receive the threaded implant.
Urbahns teaches the use of intervertebral space measuring tools and a spacer insertion device for facilitating the implantation of an intervertebral spacer (in this reference, the spacer implant is a tubular metal mesh structure which is coaxial with the patient""s spine). The measuring device described and shown in FIG. 4 in Urbahns includes a thin, elongate rod having a fixed cylindrical end having a constant and known thickness. Insertion of this measuring tool into the intervertebral space provides the physician with an approximate understanding of the size of the implant to be inserted. This measurement defines the appropriate cutting of the patient""s bone to create the desired, and necessary, space to receive the metal mesh. The measuring tool is, however, not used to distract the space.
Urbahn describes a distraction provided in conjunction with the spacer insertion instrument shown in FIGS. 13-16 of the reference. This instrument, which is more fully described and shown in FIG. 4 in Moskovich, includes a pair of flat elongate guide surfaces that are hinged at an elbow joint at the distal ends of the surfaces. The distal joint is designed to extend out of the planes defined by the longitudinal axes of the two guides. The proximal ends of the surfaces are to be placed between the collapsed bones. By virtue of the elbow joint, the surfaces are angled substantially when the metal mesh structure, or test member, is placed between the surfaces. The metal mesh (or the test member) is then hammered down the guide surfaces, prying the vertebral bodies apart.
Moskovich is generally directed to a threaded insertion device for final placement of the femoral ring (not a metal mesh structure) into the intervertebral space. A threaded shaft, having a distal ram portion and an intermediate nut, is coupled to the guide surfaces via stud-groove interfaces that engage studs on the intermediate nut and corresponding grooves on the elongate guide surfaces. The ram portion seats against the femoral ring and causes it to move relative to the guides. The space into which the femoral ring is to be inserted (as above with the metal mesh implant) must be cut to the appropriate size to receive the graft. Initially, the surgeon rotateably advances the graft into the space. Subsequent to proper placement of the graft (i.e., when the graft jams into the pre-cut receiving space), continued rotation of the shaft causes the distraction surfaces to be removed by motion of the guides relative to the shaft (the intermediate nut engages the guides and pulls them free of the vertebral bones). Failure to properly cut the space, or structural failure of the graft and/ or bone material, will prevent removal of the guides, and further rotation of the shaft will drive the allograft further than clinically desired (risking paralysis and/or damage to surrounding vessels).
Therefore, there is a need for a vertebral implant insertion device that does not require the space into which the implant is to be inserted to be cut to a specific size or shape so that the implant must jam into the space to effect the removal of the guides. There is also a need for an insertion device that does not increase the risk of structural failure of the implant during the insertion and does not depend on the structural stability of the implant to effect the insertion.
In an embodiment, the invention provides an instrument for inserting an implant between vertebral bodies. The instrument includes a holder adapted to hold the implant during insertion of the implant between the vertebral bodies, a retractor adapted to retract the holder away from the implant after the insertion, and a guard adapted to prevent the implant from being removed from between the vertebral bodies during the retraction.
In an aspect, the retractor can include a coupling adapted to couple the holder to the guard and by which relative movement between the holder and the guard can be effected during the retraction. Preferably, the retractor includes a threaded coupling that includes a bore and a screw that can thread within the bore, such that rotation of the screw within the bore effects relative movement between the holder and the guard.
In another aspect, the holder can include a plurality of arms. The guard can include a shaft adjacent the arms, the shaft having an engagement surface. The retractor can include a threaded bore and a screw that can thread within the bore, the screw having an end that engages the engagement surface of the shaft. Preferably, rotation of the screw within the bore moves the arms relative to the shaft.
In still another aspect, the guard can include a shaft having a proximal end and a distal end. The holder can include a plurality of arms, each having a distal end, the arms being adapted to cooperate to hold the implant using the distal ends of the arms such that the implant is adjacent the distal end of the shaft. The retractor can include a bore and a screw that can thread within the bore and engage the proximal end of the shaft. Preferably, rotation of the screw within the bore effects the retraction by pulling the arms alongside the shaft; and during the retraction, the distal end of the shaft can engage the implant to prevent the implant from being removed from between the vertebral bodies.
In yet another aspect, the guard can include a shaft having a longitudinal axis, a proximal end having an engagement surface, and a distal end. The holder can include a plurality of arms, each having a proximal end and a distal end and each longitudinally extending alongside the shaft, the arms being adapted to cooperate to hold the implant using the distal ends of the arms such that the implant is longitudinally adjacent the distal end of the shaft during insertion of the implant between the vertebral bodies. The retractor can include a bore in longitudinally fixed relation to the arms during the retraction and having a longitudinal axis coaxial with the longitudinal axis of the shaft during the retraction, and a screw that can thread within the bore and having a distal end that engages the engagement surface of the proximal end of the shaft during the retraction. Preferably, rotation of the screw within the bore, after the insertion of the implant between the vertebral bodies and once the distal end of the screw has engaged the engagement surface of the shaft, effects the retraction by pulling the arms alongside the shaft until the distal ends of the arms no longer hold the implant. Also preferably, during the retraction, the distal end of the shaft can engage the implant to prevent the implant from being removed from between the vertebral bodies.
Preferably, the distal ends of the arms can be opened away from one another to receive the implant, and closed toward one another to hold the implant. Also preferably, the proximal ends of the arms are joined to one another. Also preferably, each arm has an outer surface, and the instrument further includes a collar that can be slid against the outer surfaces of the arms to open and close the distal ends of the arms. Also preferably, each of the outer surfaces has a laterally outwardly tapering portion against which the collar can be slid.
Preferably, each of the distal ends of the arms includes an extension that extends beyond the distal end of the shaft, and the implant is held between the extensions. Also preferably, each extension includes a plate having a surface that contacts the implant when the implant is held. Also preferably, each plate has a lateral edge and a lateral guard at the edge to prevent the implant from laterally moving from between the plates when the implant is held. Also preferably, during the insertion, the plates can be inserted between the vertebral bodies with the implant between the plates, and during the retraction, the plates can be removed from between the vertebral bodies by the retractor. Also preferably, at least one of the extensions has a ridge for limiting the extent to which the plate of the extension can be inserted between the vertebral bodies during the insertion.
Preferably, the distal ends of the arms are adapted to adjust to accommodate the surface topography of the implant to hold the implant. Also preferably, each of the arms includes a longitudinally extending body and each of the distal ends of the arms includes an extension and a coupling whereby the extension is coupled to the body so that the extension can hinge relative to the body. Also preferably, the coupling includes a distal lateral through hole on the extension, a proximal lateral through slot on the extension, a distal lateral through hole on the body, a proximal lateral through hole on the body, a distal rod passing laterally through the distal through holes, and a proximal rod passing laterally through the proximal through hole and the proximal through slot. Also preferably, the through slot can expand to allow the extension to hinge relative to the body.
Preferably, the retractor includes a body having the bore and a coupling whereby the body is coupled to the proximal ends of the arms so that the body can hinge relative to the arms to place the bore in longitudinally fixed relation to the arms during the retraction and to align the longitudinal axis of the bore coaxial with the longitudinal axis of the shaft during the retraction. Also preferably, the coupling enables the body to hinge relative to the arms to allow access to the proximal end of the shaft. Also preferably, the body includes a trunk having the bore and the coupling includes at least one curved passageway fixed to the proximal ends of the arms and at least one corresponding hook fixed to the trunk, whereby the travel of the hook through the passageway provides a range of positions through which the trunk can hinge relative to the arms. Also preferably, one of the positions is a position in which the bore is in longitudinally fixed relation to the arms and the longitudinal axis of the bore is aligned coaxial with the longitudinal axis of the shaft. Also preferably, another of the positions is a position in which the trunk is positioned to allow access to the proximal end of the shaft.
In another embodiment, the invention again provides an instrument for inserting an implant between vertebral bodies. The instrument includes a holder adapted to hold the implant during insertion of the implant between the vertebral bodies, a retractor adapted to retract the holder away from the implant after the insertion, and a guard adapted to prevent the implant from being removed from between the vertebral bodies during the retraction.
In an aspect, the holder can include a set of tongs adapted to hold the implant. The guard can include a central rod about which the set of tongs open and close. The retractor can include a screw assembly for retracting the set of tongs away from the implant while maintaining the rod against the implant to prevent the implant from being removed from between the vertebral bodies. Preferably, the screw assembly includes a bore and a screw that can be rotated within the bore to engage the rod during the retraction and move the set of tongs relative to the shaft.
In another aspect, the holder can include a set of tongs having a proximal end and distal ends for holding the implant during the insertion of the implant between the vertebral bodies. The guard can include a central rod about which the set of tongs can open and close, the rod having a proximal end and a distal end in front of which the distal ends of the set of tongs can hold the implant during the insertion, the rod being coupled to the set of tongs to prevent lateral movement between the rod and the set and allow longitudinal movement between the rod and the set. The retractor can include a screw assembly at the proximal end of the set of tongs adapted to retract the distal ends of the set of tongs away from the implant after the insertion while allowing the distal end of the rod to be maintained against the implant during the retraction to prevent the implant from being removed from between the vertebral bodies during the retraction. Preferably, the screw assembly includes a bore longitudinally fixed to the set of tongs during the retraction and aligned with the rod during the retraction, and a screw that can be rotated within the bore to engage the proximal end of the rod during the retraction and pull the set of tongs longitudinally relative to the shaft until the distal ends of the set of tongs no longer hold the implant. Preferably, the screw can thread within the bore.
Preferably, the rod is coupled to the set of tongs by a coupling including a lateral through slot through the rod that extends longitudinally within the rod, and a pin on the set of tongs that passes laterally through the through slot and travels longitudinally within the through slot during the retraction.
Preferably, the screw assembly is coupled to the proximal end of the set of tongs so that the screw assembly can hinge relative to the set of tongs through a range of positions including a position in which the bore is longitudinally fixed to the set of tongs and aligned with the rod, and a position in which the proximal end of the rod can be accessed.
Implants that can be inserted using the invention include, but are not limited to, femoral ring allografts, bone grafts, vertebral spacers, cylindrical metallic devices (e.g., cages), metal mesh structures that may be filled with suitable bone graft materials, and other implants. Implants that can be inserted using the invention also include a spacer that is described more fully in copending application, to Thomas J. Errico and Joseph P. Errico, entitled xe2x80x9cPorous Interbody Fusion Device Having Integrated Polyaxial Locking Interference Screwsxe2x80x9d, the specification of which is incorporated herein by reference.